1. Field of the Invention
This invention relates to a motor driving control circuit suited for a camera and more particularly to a motor drive control circuit which performs a battery check during a motor drive operation and then time serially performs various control operations on the basis of information obtained by the battery check.
2. Description of the Prior Art
Cameras equipped with motor drive devices and especially with film feeding drive devices of the kind having a function called an automatic reversing or automatic returning function to automatically rewind the film when it comes to an end thereof have recently increased in number. In the camera of this kind, however, the film winding power of the motor becomes insufficient when a battery voltage drops. In that event, the on-and-off time intervals of a switch which is arranged to turn on and off at the time of feeding the film become extremely long or, in some case, a film winding process cannot be completed within a predetermined length of time. Then, since a rewinding load is generally lighter than a winding load, the camera might begin to rewind the film. In addition to this, even when the film begins to be automatically rewound after coming to the end thereof, film might come to a stop halfway in the rewinding process to be left in an incompletely rewound state by a drop in the battery voltage.
To avoid these troubles, it is conceivable to check and detect the power supply voltage in some suitable manner and to automatically inhibit film winding or automatic film rewinding, if the voltage thus detected is below a predetermined level. Meanwhile, it is of course preferable, for accurate and maximum use of the battery power, to perform a power supply voltage check under an actual load, in the same manner as in the general technical fields as well as in the field of cameras and, in this case, to perform a battery check during an actual process of power supply to the motor.
However, in accordance with the prior art, a process to be carried out after the power supply voltage is found below a predetermined level (hereinafter referred to as a battery NG state) by a voltage check performed during power supply to a motor have been not always satisfactory. More specifically stated, as shown in an example of the prior art disclosed in Japanese Laid-Open patent application No. Sho 57-151924, the battery voltage rises when power supply to the motor is cut off and this results in an erroneous action with the detected battery NG information inverted by the rise of voltage. To solve this problem, the prior art method necessitates continuation of power supply after detection of the battery NG state. However, the battery which has been found NG is fraught with such possibilities as: The continuation of power supply might cause a liquid leak; and in the event of a battery check performed under a low temperature condition or other battery power lowering conditions, the battery which is determined to be in the NG state might become serviceable again when it is brought back to a normal temperature condition. In such a case, a latent evergy of the battery might completely be consumed by the continued power supply.
Meanwhile, in another example of the prior art disclosed in Japanese Laid-Open patent application No. Sho 58-75135, the power supply voltage is determined by detecting the tension of the film. If the battery is thus found in the NG state, the NG information is stored and then the power supply to the motor is cut off. This method necessitates the use of means for detecting that the motor is stopped by the tension of the film and also use of a complex logic circuit including an oscillator, a counter, etc. In addition to them, the method requires for a practical application the provision of either a back-up power supply or boosting means for keeping these circuit elements operative in the event of a drop in the power supply voltage. Therefore, the circuit arrangement according to the method disclosed becomes complex and expensive.